It is known to add a hydrazine compound to silver halide photographic emulsions or developers. For example, U.S. Pat. No. 3,730,727 describes a developer containing ascorbic acid and hydrazine, U.S. Pat. No. 3,227,552 describes the use of hydrazine as an auxiliary developing agent for obtaining direct positive color images, U.S. Pat. No. 3,386,831 describes a silver halide photographic material containing the .beta.-monophenylhydrazide of an aliphatic carboxylic acid as a stabilizer. These techniques are also described in U.S. Pat. No. 2,419,975 and Mees, The Theory of Photographic Process, 3rd Ed., p. 281 (1966).
In particular, U.S. Pat. No. 2,419,975 discloses that high contrast negative images are obtained by the addition of a hydrazine compound.
It is also described in the foregoing patent that by developing a silver halide photographic material containing a hydrazine compound in the silver chlorobromide emulsion layer thereof with a developer having a high pH of 12.8, very high contrast photographic characteristics having a gamma of over 10 are obtained. However, a high alkaline developer having a pH near 13 is unstable and liable to be air-oxidized, and cannot be stored or used for a long period of time.
The high contrast photographic characteristics having a gamma of over 10 are very useful for the photographic reproduction of continuous tone images by dot image, which is useful for making printing plates, or the reproduction of line images. For obtaining such high contrast photographic characteristics, a method of developing a silver halide photographic material using a silver chlorobromide photographic emulsion containing more than 50 mol%, preferably more than 75 mol% silver chloride with a hydroquinone-containing developer having a very low effective concentration of a sulfite ion (usually lower than 0.1 mol/liter) has been conventionally used. However, in the method, the sulfide ion concentration in the developer is low and hence the developer is very unstable and cannot be stored longer than 3 days.
Moreover, since these methods require the use of a silver chlorobromide emulsion having a relatively high content of silver chloride, a high sensitivity can not be obtained in these methods. Accordingly, it has been greatly desired to obtain super high contrast photographic characteristics useful for the reproduction of dot images and line images using high sensitive silver halide emulsions and a stable developer.
The inventors previously disclosed silver halide photographic emulsions giving very high contrast negative photographic characteristics using stable developers in U.S. Pat. Nos. 4,224,401, 4,168,977, 4,243,739, 4,272,614, and 4,323,643. However, it has now been found that the acylhydrazine compounds used in these inventions have various disadvantages.
That is, it is known that hydrazines generate nitrogen gas during development and it sometimes happens that the nitrogen gas gathers in the photographic films during development to form bubbles therein and spoil the photographic images.
Thus, from the aspect of reducing the generation of the bubbles and reducing, at the same time, the cost for producing photographic images, a compound capable of giving very high contrast photographic characteristics with a small amount of the compound has been desired.
Also, in these conventional hydrazines, a large amount thereof is required for obtaining a high sensitivity and high contrast and in the case of requiring a particularly high sensitivity for the performance of photographic materials, it is desirable to use the hydrazines with other sensitizing techniques (for example, strengthening the chemical sensitization, the increase of silver halide grain size, and the addition of the compounds accelerating sensitivity, as described in U.S. Pat. Nos. 4,272,606 and 4,241,164, etc.), but the use of the sensitizing technique with the hydrazines sometimes cause an increase in sensitivity with the passage of time and an increase of fog during storage. Accordingly, a compound which is effective for the foregoing purpose with a very small amount thereof without causing problems in stability with the passage of time and which can be easily prepared has been desired.
On the other hand, it is described in U.S. Pat. Nos. 4,385,108 and 4,269,929 that very high contrast negative photographic characteristics are obtained by using hydrazines having a substituent capable of being easily adsorbed on silver halide grains, but in practical use of the hydrazine compounds having the foregoing substituent described in the above patent specifications, there is a problem that they cause desensitization with the passage of time during the storage of the photographic materials containing them. Accordingly, it is necessary to select a compound which does not cause such a problem.